Focus system



J. DE LEON FOCUS SYSTEM Filed Dec. 21, 1950 5500 TURNS 5900 TURNS 22 ELECTRONIC CIRCUITS 23 Fig. i

ANTENNA TELEVISION CIRCUITS CATHODE-RAY TUBE INVENTOR. JOHN DE LEON l P a w ATTORNEYS Patented Oct. 5, 1954 Zfighllt .UNITED STATES PATENT OFFICE FOCUS SYSTEM .lohn De Leon, Ridgewood, N. J assignor to Allen B. Du Mont Laboratories, Inc., Clifton, N. J a corporation of Delaware Application December 21, 1950, Serial No. 201,913

4 Claims.

connection of the potentiometer 22 across a portion of rather than the entire focus coil.

Other objects of the invention are accomplished by connecting the circuit to the focus coil in the manner shown and described, so that the focus control potentiometer 22 comprises a variable shunt resistance with respect to the inner turns i6, and does not affect the current in the outer turns 11. This manner of connection advancircuit in which the circuit resistance does not tageously utilizes the fact that the outer turns change appreciably when the focus is adjusted. i"! have a larger resistance than the inner turns A further object is to provide a circuit having l3 because the outer turns have a larger cira large range of focus adjustment. cumference and therefore greater resistance per Other objects will be apparent from the folturn. lowing disclosure, 5 By connecting the focus current adjusting con- In the drawingstrol across a portion of focus coil turns having Figure l is an electrical circuit diagram of an a relatively low ratio of resistance pe turn, embodiment of the invention; stabilization of circuit resistance is improved be- Figure 2 i a diagrammatic representation f a, cause a smaller change in the control resistance focus coil construction; and Will suflice to provide a required change in ampere Figure 3 is a side view of the focus coil positurns. Also, the range of focus adjustment is tioned on a cathode ray tube, greater for a given change in the focus control The focus coil It contains multiple turns of resistance. wire having an inner end terminal I2 and an In the preferred embodiment shown, the focus outer end terminal [3. A tap terminal [4 elec- 5 coil tap M is located at a position between the trically partitions the coil I l into two parts c0m-, resistive center and turn center of the coil. Howprising inner turns It and outer turns l1. ever, in some applications it might be desirable The focus coil II is connected in series with a to locate the tap M at a different position. fixed resistor 1%, electronic circuits l9, and a It y, under certain Conditions, be e ab e voltage source 2|. A focus control potentiometer to isolate electrically the inner turns from the 22 is connected between the tap terminal It and Outer turns, and t provide four terminals on a junction 23 between the fixed resistor 18 and the focus @011- The Outer tu ns can then be electronic circuits IS. The adjustable tap 24 of Connected to One Source Of Current, d t e inner the potentiometer 22 is connected to the inner turns can be connected to a Source Of adjustable end terminal 12 of the focus coil H. A magnetic core, not shown in the drawing, is generally em- When s g ms a agnet COHtrOI circuit in ployed t confine and t i t t focusing accordance with the present invention, the folfield. lowing criteria may be considered:

Fosus current is adjusted by means f t 1. Determine the required ampere turns for potentiometer 22. When the adjustable tap 24 40 the Outer turns H In eeeoldenee t t e mi is positioned at the end a, the inner turns l6 mum equired ma netle fieldare short circuited and current passes only Determine the required p e tu s or the through the outer turns 17 of the focus coil; this inner turns in rd ce W th the maximum is the condition for a minimum focusing magnetic Ietltlired magnetic fi making owa e for field (minimum ampere turns). To obtain the the Shunt Current that will yp through the maximum focusing magnetic field (maximum Detentlometer ampere turns), the tap 24 is positioned at the end Determine the resistance of the Potentiomb of the potentiometer 22; a portion of the eter 22 a p se amo required Wattage current then passes through the inner turns [6 at maximum required magnetic field, earand the entire current passes through the outer ity of Control, and tolerable range of Change in turns ll. The fixed resistor l8 functions to cause total circuit resistance. a more constant resistance of the focus circuit 4. Determine the valued the fixed resistance between the terminals 13 and 23 when the potenl8 to obtain optimum stability of total circuit tiometer is adjusted. The desideratum of more resistance with respect to changes in focus adconstant circuit resistance is also aided by the justment.

Although the invention is described in detail for a particular application having electronic circuits connected in series therewith, it may also be connected in parallel to a power source.

The scope of the invention is defined in the following claims.

What is claimed is:

1. Apparatus 'for producing a controlled magnetic field, comprising a @011 connected in'a series circuit, said coil having multiple turns and two end terminals, a direct current source connected to one of said end terminals and across said circuit, a tap on said coil, and current adjusting means comprising variable resistance connected directly between said tap and the other of said end terminals.

2. An adjustable magnetic focus system fora cathode ray tube comprising a coil having an inner turn portion and an outer turn portion and a tap between said inner and outer turn portions, a "fixed resistance "elefnent having one end connected to said inner turn portion, a potentiom'et'er connected between said tap and the other end of said fixed resistance element, an adjustable tap on said potentiometer connected to said inner turn portion, and a current source connected to said outer turn portion.

3. In a television receiver, a cathode ray tube and a magnetic "focus system associated therewith, said syst'em comprising a coil positioned with respect to said cathode ray tube, said coil having an inner turn portion and an outer turn portion and a tap between said inner and outer turn portions, a fixed resistance element having one end connected to said inner turn portion, a junction at the other end of said fixed resistance element, a potentiometer connected between said "tap "and said junction, as al'tlji'istalo'le 'tap on said potentiometer connected to -"said inner turn portion, electronic circuits connected to said junctibn, and a voltage source connected between said electronic circuits and said outer turn portion of said coil.

adjustable magnetic device comprising a coil having -"a tap thereon, a fixed resistance element having one end connected to an end of said coil, a potentiometer connected between said tap and the remaining end of said fixed resistance element,an adjustable tap on said potentiometer connected to said end of said coil, and a current source connected between the remaining end of said coil and said remaining end of said fixed resistance element.

References Cited in the 16 of this patent UNITED s'Tn-TE's PATENTS Number Name Date 1,914,192 Bedford June 13, 1933 2,447,804 Holst Aug. 24, 1948 

